Sometimes, the problem to be solved is simple – poor thermal performance. Although heat exchanger designers always aim for high heat transfer coefficients this can sometimes be difficult to achieve with a conventional plain tube design. In many cases this is due to the properties of the tubeside fluid such as high viscosity and/or low thermal conductivity. Occasionally, low heat transfer rates are a consequence of the arrangement of the exchanger such as when single pass tube bundles are required.
Whatever the reasons, poor tubeside performance can usually be avoided by considering the use of heat transfer enhancement technologies. Engineered devices such as hiTRAN Matrix Elements invariably provide increased heat transfer coefficients relative to plain tubes.
Graphical representation of plain tube heat transfer against hiTRAN enhanced performance range
When fluid flows through a plain tube the fluid nearest the wall is subjected to frictional drag, which has the effect of slowing down the fluid at the wall. This laminar boundary layer can significantly reduce the tubeside heat transfer coefficient and consequently, the performance of the heat exchanger.
Inserting correctly profiled hiTRAN Matrix Elements into the tube will disrupt the laminar boundary layer, creating additional fluid shear and mixing, thereby minimizing the effects of frictional drag. hiTRAN Wire Turbulators are particularly effective at enhancing heat transfer efficiency in tubes operating at low Reynolds numbers (laminar to transitional flow.) Although the heat transfer increase is greatest in the laminar flow region (up to 16 times), significant benefits can be obtained in the transitional flow regime (up to 12 times) and turbulent flow regime (up to 3 times). Cal Gavin have installed hiTRAN Systems in heat exchangers operating with Reynolds numbers from 1 to over 100,000.
Whilst there is an increase in frictional resistance associated with hiTRAN Systems, the amount of enhancement is such that solutions can be found which offer increased heat transfer at equivalent or lower pressure drop than a plain tube.
Below are some brief descriptions of projects CALGAVIN have enhanced previously. For a more comprehensive range please see the case studies page.